The disclosure relates generally to reducing radio frequency (RF) interference and more particularly to reducing RF interference in uplink RF communications signals in a remote unit in a wireless distribution system (WDS), such as a distributed antenna system (DAS).
Wireless customers are increasingly demanding digital data services, such as streaming video signals. At the same time, some wireless customers use their wireless communications devices in areas that are poorly serviced by conventional cellular networks, such as inside certain buildings or areas where there is little cellular coverage. One response to the intersection of these two concerns has been the use of DASs. DASs include remote units configured to receive and transmit communications signals to client devices within an antenna range of the remote units. DASs can be particularly useful when deployed inside buildings or other indoor environments where the wireless communications devices may not otherwise be able to effectively receive RF signals from a source.
In this regard, FIG. 1 illustrates a distribution of communications services to remote coverage areas 100(1)-100(N) of a WDS provided in the form of a DAS 102, wherein ‘N’ is the number of remote coverage areas. These communications services can include cellular services, wireless services, such RF identification (RFID) tracking, Wireless Fidelity (Wi-Fi), local area network (LAN), and wireless LAN (WLAN), wireless solutions (Bluetooth, Wi-Fi Global Positioning System (GPS), signal-based, and others) for location-based services, and combinations thereof, as examples. The remote coverage areas 100(1)-100(N) may be remotely located. In this regard, the remote coverage areas 100(1)-100(N) are created by and centered on remote units 104(1)-104(N) connected to a central unit 106 (e.g., a head-end equipment, a head-end controller, or a head-end unit). The central unit 106 may be communicatively coupled to a signal source 108, for example, a base transceiver station (BTS) or a baseband unit (BBU). In this regard, the central unit 106 receives downlink communications signals 110D from the signal source 108 to be distributed to the remote units 104(1)-104(N). The remote units 104(1)-104(N) are configured to receive the downlink communications signals 110D from the central unit 106 over a communications medium 112 to be distributed to the respective remote coverage areas 100(1)-100(N) of the remote units 104(1)-104(N). Each of the remote units 104(1)-104(N) may include an RF transmitter/receiver and a respective antenna 114(1)-114(N) operably connected to the RF transmitter/receiver to wirelessly distribute the communications services to client devices 116 within the respective remote coverage areas 100(1)-100(N). The remote units 104(1)-104(N) are also configured to receive uplink communications signals 110U from the client devices 116 in the respective remote coverage areas 100(1)-100(N) to be distributed to the signal source 108. The size of each of the remote coverage areas 100(1)-100(N) is determined by the amount of RF power transmitted by the respective remote units 104(1)-104(N), receiver sensitivity, antenna gain, and RF environment, as well as by RF transmitter/receiver sensitivity of the client devices 116. The client devices 116 usually have a fixed maximum RF receiver sensitivity, so that the above-mentioned properties of the remote units 104(1)-104(N) mainly determine the size of the respective remote coverage areas 100(1)-100(N).
To provide adequate RF coverage in the remote coverage areas 100(1)-100(N), each of the remote units 104(1)-104(N) may include one or more power amplifiers to amplify the downlink communications signals 110D prior to transmitting to the client devices 116. Each of the power amplifiers employed in the remote units 104(1)-104(N) may be configured to amplify the downlink communications signals 110D to a respective power level, depending on an intended coverage range of the downlink communications signals 110D. In this regard, some of the power amplifiers may be low-power power amplifiers that can amplify the downlink communications signals 110D up to 20 decibel-milliwatts (dBm), while some other power amplifiers may be high-power power amplifiers capable of amplifying the downlink communications signals 110D to more than 30 dBm. Notably, the high-power power amplifiers may be less linear compared to the low-power power amplifiers. As a result, the high-power power amplifiers may be more prone to generating intermodulation products and/or adjacent channel interference in the amplified downlink communications signals 110D. As such, it may be desired to improve linearity in the power amplifiers, especially in the high-power power amplifiers.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.